WHEN the vast baby-boom generation exploded into adolescence in the 1960s, marketers exulted. Advertising consultants, always eager to coin a phrase, began happily explaining to corporations the difference between “teenyboppers” and “counterculture consumers.” Over the next 40 years, as Aquarius aged and the billable hours accumulated, marketers explained that such “market segmentation” techniques were the key to untold riches.

Today, Jimi is dead, the revolution is over and fiber supplements are the pill of choice in Woodstock. But with 37 million Americans over the age of 65, and 30 million more expected to cross that thin gray line in the next decade, the boomers and older consumers still represent billions of dollars in potential sales. So once again, companies are scrambling to update their slicing and dicing of the senior marketplace.

But what they are finding, advertising executives say, is that some old tactics don’t work anymore. Older consumers don’t want to be treated like teenagers; what’s more, they don’t want to believe they fall into any niche at all.

“Seniors, particularly baby boomers, each believe they belong to a market segment made up of exactly one person,” said Blaine Branchik, an associate professor of marketing at Quinnipiac University who has studied the history of selling to the elderly. “Many believe the only thing they have in common is that they are all so unique that they have nothing in common.”

For example, Age Wave, a consulting firm, has settled on four essential categories for post-retirement consumers. There are “Ageless Explorers,” or rich retirees who respond to images of silver-haired scuba divers reinventing themselves in their waning years. The “Comfortably Contents” are also wealthy, but more attracted to scenes of fishermen, friendly dogs and rocking chairs. They want to spend their final years free from the responsibilities of work, social obligations and worrying about anyone else. The “Live for Todays” wish they could relax, but didn’t save much, so their financial anxieties make them easy targets for Costa Rican retirement communities and thrifty insurance plans. And then there are the “Sick and Tireds,” basically ready to die, who are attracted to anything that makes the waiting less painful, particularly if it costs less than $19.95.

It’s unclear how useful such labels are in selling to older consumers. What is certain is that the tactics echo those that have worked in the youth marketplace for more than 40 years. When that process began, some rules emerged. Never, for example, refer to kids as “kids.” Always develop advertisements that speak to adolescent whims but also appeal to parents, who ultimately control the checkbook. Some people believe that reasoning still holds.

“The No. 1 rule is that you never call an older buyer old,” said Joseph F. Coughlin, director of the Massachusetts Institute of Technology’s AgeLab. “And because many seniors rely on their kids for advice, it’s important to talk to the senior and the daughter who will likely make the purchase.”

But some things are very different. For instance, researchers have found that as people age, shifts in brain activity begin to affect decision making. In particular, the elderly, on average, become less adept at processing numerical information or recalling details presented in unfamiliar settings.

So even as marketers embrace market segmentation, they’ve begun looking for new research to explain how to operate in this older world.

One study, published in the Journal of Personality and Social Psychology in 2003, exposed consumers to advertisements that were identical except for the text. One ad, promoting a camera, emphasized photography’s capacity to expand horizons. “Capture the unexplored world,” it read. The other emphasized the camera’s capacity to record memories. It read, “Capture those special moments.” While middle-age and young consumers recalled both ads, elderly consumers much more easily remembered the advertisement emphasizing precious memories.

Other studies have shown that older consumers tend to ignore advertisements that warn them about the importance of saving to avert financial calamity. But they remember the same commercial when it emphasizes how thrift makes it easier to buy plane tickets to visit grandchildren.

“The health care and financial service industries for years tried to barrage customers with facts and fear,” Mr. Coughlin, of M.I.T., said. Marketers developed advertisements warning about strokes or the specter of a penniless future. But “older consumers filter out those messages,” Mr. Coughlin said.

Instead, as in the case of the camera advertisements, older consumers are attracted to images that evoke warm nostalgia and “ads that emphasize independence and fun,” Mr. Coughlin added.

There is one caveat, however: such advertisements are persuasive only as long as they avoid mentioning that a fond remembrance of things past usually requires living through a long past in the first place. “Companies that sell cars designed for old men find that no one wants to buy them, especially old men,” Mr. Coughlin said.

Consider, for instance, the Honda Element, a compact sport utility vehicle aimed at young buyers and advertised through video games, social-networking Web sites and the television show “Rock Star: Supernova.” The car is popular among young adults. It’s also a surprising seller among retirees, who like it because it is low to the ground and because the durable floors can handle gardening equipment and pets as easily as surfboards and mountain bikes.

Indeed, marketers who have tried to cater to various segments — the “Ageless Explorers” and “Comfortably Contents” — have discovered that successful segmentation has less to do with age than with how vigorously consumers want to ignore the inevitable consequences of their advancing years.

“We work to dramatically change the perception of what is old by focusing on ageless realities,” said Emilio Pardo, chief brand officer for AARP, formerly the American Association of Retired Persons. “Life is based on someone’s needs, not how many years they’ve lived. We emphasize the idea of ageless aging.”

But aging isn’t ageless forever, of course. Everyone dies, and before that most people eventually lose some of their faculties. So some people worry that as marketers get better at targeting the elderly, the line between advertising and unscrupulous manipulation will be harder to discern. There is talk of creating regulations to protect older consumers from certain types of advertising. That effort, too, has roots in baby boomers’ adolescence. Many of today’s laws regarding advertising tactics and teenagers were first discussed in the 1950s and 60s, when lawmakers began realizing that cartoon characters who smoke might unduly influence fans of the Mickey Mouse Club.

The initiatives are beginning to find some support. But unusual critics have emerged: advocates for the elderly, who worry that older Americans will encounter a prejudice that we have comfortably adopted regarding teenagers.

“We are very hesitant about any regulations that are designed to only protect people once they are over a certain age,” said Jean Setzfand, director of financial security for AARP. “Part of the hesitation is that it might reinforce the perception that seniors shouldn’t make their own decisions.”

Partly this stems from a discomfort with drawing parallels between teenagers and the elderly in the first place. Although adolescents and older consumers may have much in common, there is a big difference: one group is moving toward adulthood, the other away from their prime years.

“It’s appropriate to limit teenagers’ choices, because they are advancing towards independence,” Ms. Setzfand said. But aging, she noted, “isn’t a temporary condition; the elderly deserve more dignity than to treat them as if they’re a bunch of teens.”

And that’s the real reason that marketers’ efforts to segment the elderly might fall apart, experts say. Teenagers ultimately don’t mind belonging to a group, because there’s always the opportunity to eventually become someone new. The elderly, by definition, are running out of opportunities for reinvention.

A version of this article appears in print on , on Page 43 of the New York edition with the headline: Six Decades at the Center of Attention, and Counting. Order Reprints|Today's Paper|Subscribe